Belt unit and image forming apparatus

Abstract

A belt unit includes a first roller; a second roller; a belt extended with at least the first roller and the second roller; a first supporting member for supporting the first roller; a second supporting member disposed to be freely rotatable relative to the first supporting member for supporting the second roller; a switching member for switching the first supporting member and the second supporting member between a first state for applying tension to the belt and a second state for loosening the belt; and a regulating member for regulating the second supporting member to rotate.

What is claimed is: 
     
       1. A belt unit comprising:
 a first roller; 
 a second roller; 
 a belt extended with at least the first roller and the second roller; 
 a first supporting member for supporting the first roller; 
 a second supporting member disposed to be freely rotatable relative to the first supporting member for supporting the second roller; 
 a switching member for switching the first supporting member and the second supporting member between a first state for applying tension to the belt and a second state for loosening the belt; and 
 a regulating member for regulating the second supporting member to rotate. 
 said switching member includes a first engagement member attached to one of the first supporting member and the second supporting member to be freely rotatable and a first engaged member attached to the other of the first supporting member and the second supporting member for engaging the first engagement member so that the first supporting member and the second supporting member are maintained in the second state when the switching member rotates. 
 
     
     
       2. The belt unit according to  claim 1 , further comprising an urging member for urging one of the first supporting member and the second supporting member so that the first supporting member and the second supporting member are maintained in the second state. 
     
     
       3. The belt unit according to  claim 1 , wherein said switching member includes an engagement member attached to one of the first supporting member and the second supporting member to be freely rotatable for engaging a second engaged member so that the first supporting member and the second supporting member are maintained in the second state when the switching member rotates. 
     
     
       4. An image forming apparatus comprising the belt unit according to  claim 1 . 
     
     
       5. The image forming apparatus according to  claim 4 , further comprising an apparatus main body, said belt unit being detachably attached to the apparatus main body. 
     
     
       6. A belt unit comprising:
 a belt; 
 a first roller; 
 a second roller; 
 a first supporting member for supporting the first roller; 
 a second supporting member for supporting the second roller; and 
 a lock member disposed on the first supporting member for holding the belt unit between a first state for applying tension to the belt and a second state for loosening the belt, said lock member being arranged to switch the belt unit from the second state to the first state when the belt unit is attached to an apparatus. 
 
     
     
       7. The belt unit according to  claim 6 , wherein said lock member includes a first engagement portion for holding the first supporting member in the first state and a second engagement portion for holding the first supporting member in the second state. 
     
     
       8. The belt unit according to  claim 7 , wherein said second supporting member includes an engaged portion for engaging the first engagement portion in the second state so that the belt unit is maintained in the second state. 
     
     
       9. The belt unit according to  claim 6 , wherein said lock member is arranged to rotate toward the first supporting member so that the belt unit is maintained in the second state, and to rotate away from the first supporting member so that the belt unit is maintained in the first state. 
     
     
       10. The belt unit according to  claim 6 , wherein said first roller is arranged to increase a distance between the first roller and the second roller to extend the belt when the belt unit is switched from the second state to the first state. 
     
     
       11. The belt unit according to  claim 6 , wherein said lock member is arranged to rotate when the belt unit is attached to the apparatus. 
     
     
       12. The belt unit according to  claim 6 , wherein said first roller is arranged to increase a distance between the first roller and the second roller to extend the belt when the belt unit is attached to the apparatus. 
     
     
       13. An image forming apparatus comprising the belt unit according to  claim 6 . 
     
     
       14. The image forming apparatus according to  claim 13 , further comprising an apparatus main body, said belt unit being detachably attached to the apparatus main body. 
     
     
       15. The belt unit according to  claim 9 , wherein said lock member is arranged to rotate to protrude so that the belt unit is maintained in the second state, and is arranged to rotate to fall so that the belt unit is maintained in the first state. 
     
     
       16. A belt unit comprising:
 a belt; 
 a first roller; 
 a second roller; 
 a first supporting member for supporting the first roller; 
 a second supporting member for supporting the second roller; 
 a lock member disposed on the first supporting member for holding the belt unit between a first state for applying tension to the belt and a second state for loosening the belt; and 
 an urging member for urging the first supporting member and the second supporting member. 
 
     
     
       17. The belt unit according to  claim 16 , wherein said urging member is disposed between the first supporting member and the second supporting member. 
     
     
       18. The belt unit according to  claim 16 , wherein said urging member includes two end portions, one of said end portions abutting against the first supporting member, the other of said end portions abutting against the second supporting member. 
     
     
       19. The belt unit according to  claim 16 , wherein said lock member includes a first engagement portion for holding the first supporting member in the first state and a second engagement portion for holding the first supporting member in the second state. 
     
     
       20. The belt unit according to  claim 16 , wherein said lock member is arranged to rotate toward the first supporting member so that the belt unit is maintained in the second state, and to rotate away from the first supporting member so that the belt unit is maintained in the first state. 
     
     
       21. The belt unit according to  claim 16 , wherein said first roller is arranged to increase a distance between the first roller and the second roller to extend the belt when the belt unit is switched from the second state to the first state. 
     
     
       22. The belt unit according to  claim 16 , wherein said lock member is arranged to rotate when the belt unit is attached to an apparatus. 
     
     
       23. The belt unit according to  claim 16 , wherein said first roller is arranged to increase a distance between the first roller and the second roller to extend the belt when the belt unit is attached to an apparatus. 
     
     
       24. The belt unit according to  claim 19 , wherein said lock member is arranged to rotate to protrude so that the belt unit is maintained in the second state, and is arranged to rotate to fall so that the belt unit is maintained in the first state. 
     
     
       25. An image forming apparatus comprising the belt unit according to  claim 16 . 
     
     
       26. The image forming apparatus according to  claim 25 , further comprising an apparatus main body, said belt unit being detachably attached to the apparatus main body.